Development and testing of vanadium alloys for fusion applications

Vanadium-base alloys are promising candidate materials for application in fusion reactor first-wall and blanket structure because of several important advantages, i.e., inherently low irradiation-induced activity, good mechanical properties, good compatibility with lithium, high thermal conductivity, and good resistance to irradiation-induced swelling and damage. To screen candidate alloys and develop an optimized vanadium-base alloy, extensive investigations of physical and mechanical properties of various V-Ti, V-Cr-Ti, and V-Ti-Si alloys have been conducted before and after irradiation in lithium environment in fast fission reactors. From these investigations, a V-4Cr-4Ti alloy containing 500-1000 wppm Si and < 1000 wppm O + N + C has been identified as the most promising alloy, end more comprehensive testing on the performance of this alloy is being conducted for fusion-relevant conditions. Major results of the comprehensive work to develop the optimal alloy and test the irradiation performance are presented in this paper. The reference alloy V-4Cr-4Ti exhibited the most attractive combination of the mechanical and physical properties that are prerequisite for first-wall and blanket structures, i.e., good thermal creep behavior, good tensile strength and ductility, high impact energy, excellent resistance to swelling, and very low ductile-brittle transition temperature before and after irradiation. The alloy was highly resistant to irradiation-induced embrittlement in Li at 420-600 degrees C, and the effects of dynamically charged helium on swelling and mechanical properties were insignificant. However, several important issues remain unresolved, e.g., welding, low-temperature irradiation properties, helium effect at high dose and high helium concentration, irradiation creep, and irradiation performance in air or helium environment. Initial results of investigation of some of these issues are also given.